9.7.1 Selective Accept

[This form of the select_statement
allows a combination of waiting for, and selecting from, one or more
alternatives. The selection may depend on conditions associated with
each alternative of the selective_accept.
]

Open accept_alternatives
are first considered. Selection of one such alternative takes place immediately
if the corresponding entry already has queued calls. If several alternatives
can thus be selected, one of them is selected according to the entry
queuing policy in effect (see 9.5.3 and D.4).
When such an alternative is selected, the selected call is removed from
its entry queue and the handled_sequence_of_statements
(if any) of the corresponding accept_statement
is executed; after the rendezvous completes any subsequent sequence_of_statements
of the alternative is executed. If no selection is
immediately possible (in the above sense) and there is no else part,
the task blocks until an open alternative can be selected.

Ramification: In the absence of a requeue_statement,
the conditions stated are such that a terminate_alternative
cannot be selected while there is a queued entry call for any entry of
the task. In the presence of requeues from a task to one of its subtasks,
it is possible that when a terminate_alternative
of the subtask is selected, requeued calls (for closed entries only)
might still be queued on some entry of the subtask. Tasking_Error will
be propagated to such callers, as is usual when a task completes while
queued callers remain.